if, elif and else

2 min read 6 runnable examples Quiz included

An if statement runs a block of code only when a condition is true.

Python

temperature = 34
if temperature > 30:
    print("It's a hot day.")
    print("Stay hydrated!")
print("Have a good day.")

Notice the colon and the indented block. Change the temperature to 20 and run it again.

else

else gives the code to run when the condition is false:

Python

age = int(input("Age: "))
if age >= 18:
    print("You can vote.")
else:
    print(f"You can vote in {18 - age} year(s).")

elif

elif ("else if") checks further conditions. Python tests them top to bottom and runs only the first block whose condition is true:

Python

score = 72

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

print("Grade:", grade)

Order matters. If the score >= 60 test came first, a score of 95 would get a "D".

Nested conditions

An if can sit inside another if:

Python

has_account = True
password_ok = False

if has_account:
    if password_ok:
        print("Welcome back!")
    else:
        print("Wrong password.")
else:
    print("Please sign up.")

Deep nesting gets hard to read; often and or an early elif makes it flatter.

Conditional expressions

For simple choices there is a one-line form: value_if_true if condition else value_if_false.

Python

n = 7
kind = "even" if n % 2 == 0 else "odd"
print(n, "is", kind)

items = 1
print(f"{items} item{'s' if items != 1 else ''}")

An empty block

A block cannot be empty. Use pass as a placeholder while you are still writing:

Python

logged_in = False
if logged_in:
    pass   # TODO: show the dashboard
else:
    print("Please sign in")

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